1. Field of the Invention
The present invention relates to a brushless motor used in a spindle motor or fan motor in which a disk is driven by a disk drive. More specifically, it relates to a brushless motor provided with an oil-leak prevention means for preventing lubricating oil used in a bearing part thereof from leaking to the outside of the motor.
2. Background Art
A variety of configurations have been used heretofore for brushless motors used in disk drives and the like. FIG. 3 shows such a motor of a relatively low price. In the portion of FIG. 3 to the right of the central line, a cross-sectional view of elements are indicated by shading.
The legend 2 designates a rotor that rotates with a rotary shaft 1. This rotor 2 includes a cylindrical cap-shaped rotor case 3, a magnet 4 attached to the entire periphery of the rotor case 3, and an attraction magnet 5 that impels the rotor 2 in the downward direction in the figure.
A bearing holder 7 is fixed to a stator base 6 for example by caulking. A bearing 8 is inserted into the bearing holder 7 and rotatably supports the rotary shaft 1. The bearing holder 7 is closed at the end toward the bottom of the figure, and it supports the bottom end of the rotary shaft 1 via a thrust reception sheet 13.
On the outer periphery of the bearing holder 7, a stator core 9 around which a coil 10 is wound is fixed, and the terminal of the coil 10 is connected by soldering or the like to a connection pattern not shown in the figure of a flexible base 12 provided on the upper surface of the stator base 6.
The lower side of the bearing 8 (i.e., the stator base side), because it has a recessed portion 19 in the inside central portion thereof, has a small-diameter portion 18 with a smaller diameter than other portions. Because of the recessed portion 19, the rotary shaft 1 is rotatably supported by the portions near both end parts of the bearing 8.
Below the bearing 8 a slip-off prevention washer 11 works together with a groove 14 provided on the rotary shaft 1 to prevent the rotor 2 from slipping off.
An attraction plate 20 is fixed on the upper end part of the bearing holder 7 as seen in the figure. This attraction plate works with an attraction magnet 5 to generate attractive magnetic force, impelling the rotor 2 downward. The reason for this is to always impel the rotor in the downward direction (i.e., the thrust direction) and to prevent vibration in the rotor and drive shaft thrust direction when the rotor is used at fast revolutions. This attraction plate 20 also prevents lubricating oil that has penetrated into the bearing 8 from scattering.
Many patent applications disclose a rotor having a configuration such that a bearing is provided with lubricating oil scattering prevention means, for example, JP 11-89172A and JP 2003-32932A.
In the configuration disclosed in JP 11-89712A, a recess is provided in the upper part of a bearing for storing lubricating oil (which lowers the pressure of the oil passing through gap 24), and a scattering prevention means (sealing means 20 constituted between an extension part 23 and bearing 11) surrounding a bearing is further provided on a turntable.
In the configuration disclosed in JP 2003-32932A, slip-off prevention means is provided facing the upper end part of a bearing, and this is used as lubricating oil scattering prevention means (engaging part 14 of slip-off prevention member 7 and engaged part 12 of protrusion 20 and bearing 8).
Both of these configurations are provided for the purpose of preventing the leaking and scattering of lubricating oil from a bearing.
However, because a configuration is needed on both the stator side and rotor side in order to constitute these scattering prevention means, a gap is unavoidably provided between the configuration on the bearing side and the configuration on the rotor side.
In such cases, if these motors are attached to devices in which they are to be contained in an upright manner, and the devices are used in a still condition, then there is no problem, but if for example, the motor is attached to a portable device and is used in a state in which it is subject to change in posture and impact, there will be cases where lubricating oil leaks from the aforementioned gap.
Further, when the motor is driven, lubricating oil that has leaked out from the scattering prevention means is scattered outwardly by centrifugal force due to the rotation of the rotor, and is scattered through the rotor downwardly by and to the outside.